The invention is based on a method and a device for detecting incorrect polarity in a signal transducer, in particular in an inductive sensor according to the general class of the primary claim.
Signal transducers, in particular the types that operate according to the principle of induction, are used today for the most diverse applications. For example, inductive signal transducers are used to register the speed or angle of rotating shafts. Signal transducers are used in particular to register the angle of the crankshaft or another shaft in a motor vehicle, in which said signal transducers a stationary sensor scans the rotating shaft or a toothed rotor interconnected with the rotating shaft. The toothed rotor thereby comprises a plurality of angular points on its surface; when it moves past the sensor, AC voltage having positive and negative half-waves is induced in the sensor. This AC voltage is a direct representation of the surface of the toothed rotor. The voltage is typically converted into square-wave voltage to improve further processing. For this purpose, it is compared, in a processing circuit, with specifiable threshold values and, every time such a threshold value is reached, the level of the square-wave output signal changes. Since the fact as to whether or not the high signal level is caused by a rising flank or a falling flank of an angular point is essential to the evaluation of this signal, e.g., in an engine control unit or a microprocessor, monitoring must be performed to determine if the transducer is mispolarized or not. This is necessary because an inductive transducer typically has two connection possibilities.
A method and a device for detecting the correct or incorrect polarization of signal transducers is made known in DE-OS 197 23 866. In the case of this known method and the known device, it is assumed that the toothed rotor to be scanned comprises a plurality of identical angular points, whereby the angular points are designed so that the signal generated in the sensorxe2x80x94after conversion into a square-wave signalxe2x80x94has a curve that depends on the direction of movement. Two threshold values are taken into consideration when the output signal from the sensor is converted into the square-wave signal; every time said threshold values are reached, a signal-level reversal is triggered.
The method according to the invention and the device according to the invention for detecting incorrect polarity in a signal transducer have the advantage that they operate very reliably and can be used with any toothed rotor having a number of identical angular points and one reference point, whereby no special requirements are placed on the form of the angular points or the length of the angular points based on the intervals between the angular points. The method according to the invention or the device according to the invention can be used particularly advantageously in conjunction with a toothed rotor of the type that is standard today in internal combustion engines. Such a toothed rotor comprises 60-2 angular points distributed uniformly on its surface, and the reference point is formed by the two missing angular points. Such an xe2x80x9cincremental rotorxe2x80x9d is used to register the angle of the crankshaft of the internal combustion engine. The evaluation of the angle measurement is carried cut in the control unit of the internal combustion engine. In addition to this evaluation procedure, incorrect polarity of the transducer can be detected according to the invention. In particularly advantageous fashion, this detection of incorrect polarity takes place independently of the rest of the signal evaluation. The conditions under which the detection of incorrect polarity are to be carded out can be applied in advantageous fashion. One of these conditions can be a specifiable speed range, for example, or the detection of incorrect polarity is carried out only when the internal combustion engine is in an overrun state, or only when speed is constant, or only if the speed fluctuations remain within specifiable limits.
In a further particularly advantageous fashion, time measurements are carried out between specifiable angular points to detect mispolarization, whereby certain time windows are set, for example, within which the expected signal flank must appear if mispolarization is not present.
Further advantages of the invention are obtained by means of the measures described in the dependent claims.
An exemplary embodiment of the invention is shown in the figures in the drawing and will be explained in greater detail in the subsequent description. In particular, FIG. 1 shows the components of a system for controlling an internal combustion engine that are most important to understanding the invention, in which said system the device according to the invention or the method according to the invention can preferably be used. FIGS. 2A-2E show various signal curves that are obtained in the case of non-incorrect polarity or incorrect polarity transducers. The associated angular paints of the toothed rotor are also shown. FIGS. 3A-3C show further signal curves.